This invention relates to method of making electrodeposited copper foil, more particularly to method of making electrodeposited copper foil suitable for a printed circuit
An electrodeposited copper foil for a printed circuit has been commercially manufactured by contacting electrolytic solution of copper sulfate aqueous solution with an insoluble anode such as lead and cathode rotary drum made of stainless steel or titanium, to get copper electrodeposited copper on the cathode drum and winding it continuously.
Generally, when an aqueous solution contains only a copper ion and sulfuric acid ion as an electrolytic solution, pin hole or microporosity is generated on the copper foil due to dust or oil involuntarily existing in the system and causes serious problems for practical use. Also, the shape of promortories of a matte side which contacts with the electrolytic solution deforms so that sufficient adhesion strength cannot be obtained when adhering the foil to an insulating material at later stage. Further, it causes the problem that roughness becomes so large that insulation resistance between conductor layers or circuit conductivity becomes low, or transfer of copper to the unwanted portion of copper and undercut of the conductor after etching are increased whereby various properties as the printed are damaged.
In order to prevent the pinhole, a chlorine ion is added in the electrolytic solution, or the electrolytic solution is filtered by passing it through a filter containing an activated carbon to remove dust and oils. Also, for preventing microporosity and improving the shape of the matte side promontories, glue has heretofore been added to the electrolytic solution and it has been proposed to add various organic, inorganic materials as additives other than glue.
However, a material which is industrially more excellent than glue has never been discovered in the point of quality stabilities of a copper foil obtained therefrom.
In recent years, developments in electronic circuit technology including a semiconductor and integrated circuit are remarkable, and in the printed circuit board, boards such as single-sided and double-sided boards to multilayer boards having tens of layers have been practiced for general-purpose because of improvement in each technology such as insulation, laminating, drilling, interlayer connection, etching, component mounting, heat dissipation and printed board inspection systems. As the technology movement, since high density wiring has increasingly demanded, tendencies of highly multilayered, fine pattern and large-sized board are becoming remarkable.
For high multilayer, an insulating layer and a conductor should be made thin. For fine patterning, it is required to make a conductor thin, prevent foil crack and decrease undercut at etching. Also, for large-sizing of the multilayer board, dimensional stability is necessary. Thus, for the copper foil itself as the conductive foil, it has been required characteristics such as improved insulating and dielectric characteristics, decreased conductor resistance and low profile (decrease in roughness) of the matte side to reduce undercut as well as improved high temperature elongation to prevent foil crack due to thermal stress.
Low profiling of the matte side can be accomplished, for example, by adding a large amount of glue as mentioned above to the electrolytic solution, but accompanying increase of the amount added, rooml temperature and high temperature elongation are abruptly lowered. On the other hand, a copper foil obtained from an electrolytic solution containing no glue which is passed through an activated carbon filter has extremely high elongation at room temperature and high temperature, but shape of the promontories deforms and roughness becomes large. Further, when electrodeposited current density is suppressed to low, the resulting foil has low profile and is improved in elongation as compared with a foil prepared with high current density. However, it is hard to make uniform the low profile with a desired degree and productivity becomes low whereby it is not preferred from an economical view. As stated above, an electrodeposited copper foil having both of the low profiled matte side and a high elongation at high temperature satisfying the requirement in high density wiring can hardly be produced industrially by the prior art.